1. Field of the Invention
This invention generally relates to semiconductor devices and fabrication methods therefor, and more particularly, to a GaN-based semiconductor device and a fabrication method therefor.
2. Description of the Related Art
The semiconductor device that employs a GaN-based semiconductor is utilized as a power device that operates at a high frequency and high power. For instance, an FET such as High Electron Mobility Transistor (HEMT) is known as a semiconductor device suitable for amplifying at high frequency bands, in particular, of microwave, sub-millimeter wave, and millimeter wave.
With respect to an FET that employs the GaN-based semiconductor such as HEMT, in other words, a GaN-based HEMT, the research and development is enhanced to realize the operation at a higher frequency and higher power. For this reason, there is a need for improving mutual inductance and drain breakdown voltage. Japanese Patent Application Publication No. 2002-16245 discloses the GaN-based semiconductor HEMT (hereinafter, referred to as conventional art) in FIG. 8. A recess portion is formed in an AlGaN electron supply layer and a gate electrode is connected to a source electrode in the recess portion.
According to the conventional art, however, the gate electrode is provided on a bottom surface of the recess portion. Therefore, if the drain breakdown voltage is increased, the mutual conductance (gm) will be decreased in the HEMT having a low threshold voltage. In this case, it is possible to operate at a high power, yet it is suitable for the operation at a high frequency.